A Guide to the Scientific Knowledge of Things Familiar

Part I.--Heat.

I.--The SUN a source of heat

II.--ELECTRICITY a source of heat Thunder and lightning

III.--CHEMICAL ACTION a source of heat III.--Combustion IV.--Smoke and smoky chimneys V.--Lamps and candles VI.--Animal heat

VII.--MECHANICAL ACTION a source of heat VII.--Percussion VIII.--Friction VIII.--Compression

IX.--EFFECTS OF HEAT X.--Expansion XI.--Liquefaction XI.--Vaporization (clouds) XII.--Evaporation

XIII.--COMMUNICATION OF HEAT XIII.--Conduction XIV.--Absorption XV.--Reflection XVI.--Radiation (dew) XVII.--Convection (boiling)

Part Ii.--Air.

XVIII.--AIR Rust Tarnish

XIX.--CARBONIC ACID GAS Froth Effervescence Fermentation, &c.

XX.--CARBURETTED HYDROGEN GAS Fire damp Safety lamp

XXI.--PHOSPHURETTED HYDROGEN GAS Ignis fatuus Ghosts

XXII.--WIND

XXIII.--BAROMETER Ten special Rules

XXIV.--SNOW. HAIL. RAIN

XXV.--WATER

XXVI.--ICE Frost Freezing mixtures

XXVII.--LIGHT Reflection Telescopes Refraction Spectacles Rainbows Colour

XXVIII.--SOUND Ear trumpets Echoes

XXIX.--MISCELLANEOUS Attraction Anti-putrescents Sleep Dreams Glossary Index

PART I.

HEAT.

INTRODUCTION.

Q. What is heat?

A. The sensation of warmth.

Q. How is this sensation produced?

A. When we touch a substance of higher temperature than ourselves, the warmer substance keeps parting with its heat, till both are of equal temperature.

Q. What is that "stream of heat" called, which flows thus, from one body, to another?

A. CALO'RIC. Caloric, therefore, is the matter of heat, which passes from body to body; but HEAT is the sensation, of warmth, produced by the influx of Calo'ric.

Q. What are the four principal SOURCES of heat?

A. 1.--The Sun. 2.--Electricity. 3.--Chemical Action: and 4.--Mechanical Action.

Q. What are the principal EFFECTS of heat?

A. Expansion, Liquefaction, Vaporization, and Ignition.

CHAPTER I.. Q. _what Is The_ Principal _source of Heat_?

Q. What is the PRINCIPAL source of Heat?

A. The SUN.

Q. Why do BURNING GLASSES set fire to substances submitted to their power?

A. The rays of the sun, collected by the Burning Glass, are all bent to one point, called the "focus;" thus the heat and light, (which should be diffused over the whole glass,) being gathered together into one point, are very greatly increased.

Q. Why is there a DARK RIM round this focus?

A. Because the rays of light, which should have fallen there, are bent into the focus, and the space around, (being deprived of these rays) is accordingly darkened.

Q. Are ALL the rays bent into one point?

A. No, not quite all: and, therefore, the rim round the focus is only slightly shadowed.

CHAPTER II.. Q. _what Is the Second Chief Source of Heat?_

Q. What is the second chief source of heat?

A. ELECTRICITY.

Q. What is LIGHTNING?

A. Lightning is only an Electric Spark, taken from the clouds.

Q. What causes the discharge of an electric cloud?

A. When a cloud, overcharged with electric fluid, approaches another which is under-charged, the fluid rushes from the former into the latter, till both have the same quantity.

Q. Is there any OTHER cause of lightning, besides the one just mentioned?

A. Yes; sometimes mountains, trees, and steeples, will discharge a lightning cloud floating near; and sometimes electric fluid rushes out of the earth, into the clouds.

Q. What produces ELECTRICITY in the CLOUDS?

A. 1st--The evaporation from the earth's surface.

2ndly--The chemical changes perpetually going on: and

3rdly--Currents of air of unequal temperature, excite electricity by friction, as they pass by each other.

Q. How HIGH are the LIGHTNING-CLOUDS from the earth?

A. Electrical clouds are the lowest of all clouds; they are rarely more than 700 yards above the ground; and sometimes, they actually touch the earth with one of their edges.

Q. How high are the clouds generally?

A. In a fine day, the clouds are often 4 or 5 miles above our head; but the average height of the clouds is from 1-1/2 to 2 miles.

Q. Why is lightning sometimes FORKED?

A. When the lightning-cloud is a long way off, the resistance of the air is so great, that the electrical current is diverted into a zig-zag course.

Q. Why does the resistance of the air make the lightning zig-zag?

A. As the lightning condenses the air, in the immediate advance of its path; it keeps flying from side to side, in order to pass where there is the least resistance.

Q. How does lightning CONDENSE the air in the immediate advance of its path?

A. The air is condensed by the rapidity of the lightning-flash.

Q. Why is FORKED LIGHTNING more DANGEROUS than a straight flash?

A. Whatever resists the flash, diverts its course; and when terrestrial objects offer resistance to the current, they are in great danger of being destroyed.

Q. Why are there sometimes TWO flashes of forked lightning at the same moment?

A. Sometimes (in very severe storms) a flash of lightning will divide into two or more parts; and then each branch assumes the zig-zag form.

Q. Why is the FLASH sometimes quite STRAIGHT?

A. When the lightning-cloud hovers near the earth, as the flash meets with very little resistance, it is not diverted; or (in other words) the flash is straight.

Q. What is the cause of SHEET LIGHTNING?

A. It is only the reflection of distant flashes, not distinctly visible: and sometimes several flashes (from different clouds) intermingle, and form one vast blaze or sheet of lightning.

Q. Which FORM of lightning is the most DANGEROUS?

A. The ball of fire is by far the most dangerous; and the zig-zag lightning is next in danger. Sheet lightning is not often attended with danger.

Q. Why are BALLS OF FIRE so very dangerous?

A. Because (whenever they fall) much mischief is occasioned by their bursting, which they always do, with an explosion like that of a cannon.

Q. Do these BALLS OF LIGHTNING ever run along the ground?

A. Yes; they often run a considerable way along the ground, then stop for a little time, and burst in numberless pieces: sometimes each of these pieces will explode; and at other times, the whole ball will burst at once, producing most mischievous consequences.

Q. What mischief will these balls of fire produce?

A. They will set houses and barns on fire; and kill all cattle and human beings, which happen to be in their course.

Q. Why does LIGHTNING sometimes KILL men and beasts?

A. When the electric current passes through a man or beast, it produces so violent an action upon the nerves, that it destroys life.

Q. When is a person struck dead by lightning?

A. Only when his body forms a part of the lightning's path: i. e. when the electric fluid (in its way to the earth) actually passes through his body.

Q. Why are MEN sometimes MAIMED by lightning?

A. Because lightning strikes with amazing force, whatever opposes it: and if a man stand in the way, it strikes him such a blow, as to maim him.

Q. What is THUNDER?

A. Lightning parts the air through which it passes; and when the parted air closes again, the noise made by the concussion, is called Thunder.

Q. Why does lightning PART the air through which it passes? It does not part a rod of iron.

A. Iron is a conductor, and therefore allows the fluid to go freely through it: but air being a non-conductor, resists the lightning; which, therefore, rips it open, in order to pass through it.

Q. Why is THUNDER sometimes ONE VAST CRASH?

A. When the lightning-cloud is near the earth, as the flash is straight,--the whole volume of air (through which it passes) collapses at once; and produces one unbroken sudden crash.

Q. What is meant by the air collapsing?

A. When the rent air closes again, it is said to collapse.

Q. Why is the PEAL sometimes an IRREGULAR mangling broken ROAR?

A. When the lightning-cloud is a long way off, as the flash is zigzag, the air does not collapse all at once; and as we hear the concussion of one part after another, the peal is broken, protracted, and irregular.

Q. Which part of the collapsing air do we hear first?

A. That part nearest the earth; then the strata above; and last of all, that in the immediate vicinity of the cloud.

Q. What is meant by "STRATA of air?"

A. If a board were laid upon the earth, and several other boards were piled upon it, this pile would represent strata of wood.

Q. How does this illustration apply to the air?

A. A layer of air covers the earth; another layer rests upon it; and thus layer is piled upon layer, for 50 miles in height. Each layer is a "stratum" of air; and the plural of stratum is strata.

Q. Why do we hear the collapsing of the air NEAREST the earth FIRST?

A. Because sound takes a whole second of time to travel 380 yards; but the air is ripped from top to bottom instantaneously: if, therefore, the cloud were 1000 yards off, we should hear the collapsing of the lowest strata nearly three seconds, before we heard that in the immediate vicinity of the cloud.

Q. Why is the THUNDER sometimes like a deep GROWL?

A. When the storm is far distant, the thunder sounds like a deep growl.

Q. Does not SCENERY affect the sound of thunder?

A. Yes; the flatter the country, the more unbroken the peal: Mountain scenery breaks the peal, and makes it harsh and irregular.

Continue reading A Guide to the Scientific Knowledge of Things Familiar free in the Wunder reader →